Apparatus and method for controlling internal combustion engine

Abstract

Gas containing fuel vapor is purged as purge gas from a canister to an intake passage through a purge line. An ECU computes purge flow rate, which is the flow rate of the purge gas, and computes vapor concentration, which is the concentration of the fuel vapor contained in the purge gas. The ECU obtains a concentration correction value in accordance with the rate of change of the computed purge flow rate. The ECU correct the computed vapor concentration by using the concentration correction value and by taking into consideration of the time at which the purge flow rate is computed and the time at which purge gas having the computed flow rate is drawn into the combustion chamber. The ECU sets the fuel supply amount in accordance with the computed purge flow rate and the corrected vapor concentration. As a result, the accuracy of the air-fuel ratio control during purging is improved.

What is claimed is:  
     
       1. An apparatus for controlling the air-fuel ratio of air-fuel mixture drawn into a combustion chamber of an engine, wherein an intake passage of the engine is connected to a canister by a purge line, wherein the canister adsorbs fuel vapor generated in the fuel tank and permits the adsorbed fuel vapor to be separated, wherein gas containing fuel vapor is purged as purge gas from the canister to the intake passage through the purge line, the apparatus comprising: 
       a purge controlling device for adjusting purge flow rate, which is the flow rate of the purge gas flowing through the purge line;  
       a sensor for detecting the air-fuel ratio of the air-fuel mixture;  
       a computer for setting the amount of fuel supplied to the combustion chamber such that the detected air-fuel seeks a target air-fuel ratio;  
       wherein the computer computes the purge flow rate based on the state of the purge controlling device, and computes vapor concentration, which is the concentration of the fuel vapor contained in the purge gas, based on the difference between the detected air-fuel ratio and the target air-fuel ratio;  
       wherein, in accordance with changes of the computed purge flow rate, the computer obtains a concentration correction value for correcting the computed vapor concentration;  
       wherein, by taking into consideration of the difference between the time at which the purge flow rate is computed and the time at which purge gas having the computed flow rate is drawn into the combustion chamber, the computer corrects the computed vapor concentration by using the concentration correction value; and  
       wherein the computer sets the fuel supply amount in accordance with the computed purge flow rate and the corrected vapor concentration.  
     
     
       2. The apparatus according to  claim 1 , wherein the computer computes a delay time, which reflects the time difference, in accordance with the speed of the engine. 
     
     
       3. The apparatus according to  claim 2 , wherein the computed delay time decreases as the engine speed increases. 
     
     
       4. The apparatus according to  claim 2 , wherein the computer stores a plurality of time-sequential values of the concentration correction value, and wherein the computer selects one of the stored time-sequential concentration correction values that corresponds to the computed delay time and uses the selected concentration correction value for correcting the computed vapor concentration. 
     
     
       5. The apparatus according to  claim 4 , wherein the computer selects an older one of the concentration correction values for a greater value of the computed delay time. 
     
     
       6. The apparatus according to  claim 2 , wherein the computer stores a plurality of time-sequential values of the computed purge flow rate, and wherein the computer selects one of the stored time-sequential purge flow rates that corresponds to the computed delay time as an actual purge flow rate and uses the actual purge flow rate for setting the fuel supply amount. 
     
     
       7. The apparatus according to  claim 6 , wherein the computer selects an older one of the computed purge flow rates for a greater value of the computed delay time. 
     
     
       8. The apparatus according to  claim 1 , wherein, the computer sets the concentration correction value such that the correction amount of the computed vapor concentration, which is obtained by using the concentration correction value, gradually approaches zero as time elapses after the computed purge flow rate is changed. 
     
     
       9. The apparatus according to  claim 8 , wherein the computer sets the concentration correction value such that the degree of change of the correction amount of the computed vapor concentration, which is obtained by using the concentration correction value, changes according to the computed purge flow rate. 
     
     
       10. The apparatus according to  claim 1 , wherein the computer computes a feedback correction value based on the difference between the detected air-fuel ratio and the target air-fuel ratio, wherein the feedback correction value is used for feedback correcting the fuel supply amount, and wherein the computer computes the vapor concentration according to the feedback correction value. 
     
     
       11. An apparatus for controlling the air-fuel ratio of air-fuel mixture drawn into a combustion chamber of an engine, wherein an intake passage of the engine is connected to a canister by a purge line, wherein the canister adsorbs fuel vapor generated in the fuel tank and permits the adsorbed fuel vapor to be separated, wherein gas containing fuel vapor is purged as purge gas from the canister to the intake passage through the purge line, the apparatus comprising: 
       a purge control valve for adjusting purge flow rate, which is the flow rate of the purge gas flowing through the purge line;  
       a sensor for detecting the air-fuel ratio of the air-fuel mixture;  
       a computer for setting the amount of fuel supplied to the combustion chamber such that the detected air-fuel seeks a target air-fuel ratio;  
       wherein the computer computes the purge flow rate based on the opening degree of the purge control valve, and computes vapor concentration, which is the concentration of the fuel vapor contained in the purge gas, based on the difference between the detected air-fuel ratio and the target air-fuel ratio;  
       wherein, in accordance with the rate of change of the computed purge flow rate, the computer obtains a concentration correction value for correcting the computed vapor concentration, and stores a plurality of time-sequential values of the obtained concentration correction value;  
       wherein the computer computes a delay time according to the speed of the engine, the delay time reflecting the difference between the time at which the purge flow rate is computed and the time at which purge gas having the computed flow rate is drawn into the combustion chamber;  
       wherein the computer selects one of the stored time-sequential concentration correction values that corresponds to the computed delay time and uses the selected concentration correction value for correcting the computed vapor concentration; and  
       wherein the computer sets the fuel supply amount in accordance with the computed purge flow rate and the corrected purge concentration.  
     
     
       12. The apparatus according to  claim 11 , wherein the computed delay time decreases as the engine speed increases. 
     
     
       13. The apparatus according to  claim 11 , wherein the computer selects an older one of the concentration correction values for a greater value of the computed delay time. 
     
     
       14. The apparatus according to  claim 11 , wherein the computer stores a plurality of time-sequential values of the computed purge flow rate, and wherein the computer selects one of the stored time-sequential purge flow rates that corresponds to the computed delay time as an actual purge flow rate and uses the actual purge flow rate for setting the fuel supply amount. 
     
     
       15. The apparatus according to  claim 14 , wherein the computer selects an older one of the computed purge flow rates for a greater value of the computed delay time. 
     
     
       16. The apparatus according to  claim 11 , wherein the computer sets the concentration correction value such that the correction amount of the computed vapor concentration, which is obtained by using the concentration correction value, gradually approaches zero as time elapses after the computed purge flow rate is changed. 
     
     
       17. The apparatus according to  claim 16 , wherein the computer sets the concentration correction value such that the degree of change of the correction amount of the computed vapor concentration, which is obtained by using the concentration correction value, changes according to the computed purge flow rate. 
     
     
       18. The apparatus according to  claim 11 , wherein the computer computes a feedback correction value based on the difference between the detected air-fuel ratio and the target air-fuel ratio, wherein the feedback correction value is used for feedback correcting the fuel supply amount, and wherein the computer computes the vapor concentration according to the feedback correction value. 
     
     
       19. A method for controlling the air-fuel ratio of air-fuel mixture drawn into a combustion chamber of an engine, wherein an intake passage of the engine is connected to a canister by a purge line, wherein the canister adsorbs fuel vapor generated in the fuel tank and permits the adsorbed fuel vapor to be separated, wherein gas containing fuel vapor is purged as purge gas from the canister to the intake passage through the purge line, the method comprising: 
       adjusting purge flow rate, which is the flow rate of the purge gas flowing through the purge line, with a purge controlling device;  
       detecting the air-fuel ratio of the air-fuel mixture;  
       computing the purge flow rate based on the state of the purge controlling device;  
       computing vapor concentration, which is the concentration of the fuel vapor contained in the purge gas, based on the difference between the detected air-fuel ratio and the target air-fuel ratio;  
       obtaining a concentration correction value in accordance with changes of the computed purge flow rate;  
       correcting the computed vapor concentration by using the concentration correction value and by taking into consideration of the difference between the time at which the purge flow rate is computed and the time at which purge gas having the computed flow rate is drawn into the combustion chamber; and  
       setting the amount of fuel supplied to the combustion chamber in accordance with the computed purge flow rate and the corrected vapor concentration such that the detected air-fuel ratio seeks a target air-fuel ratio.